Apparatus for treatment of fluids requiring sterilization or pasteurization



July 16, 1957 STERILIZATION OR PASTEURIZATION W. H. COULTER APPARATUSFOR TREATMENT OF FLUIDS REQUIRING Original Filed Aug. 24. 1951 RAW MILK,n GAL/SEC. 20 J 1 (F 22 V3 GAL. sac. WATER conccmen4en MILK r N/3 GAL/554 12mm: j 2 1.

MXER l HEATER .28 Z /s GAL/SEC- 30 CONCENTRATED MILK I I HOLD\NG co'oLERvuc-r j 31 I l WATER N/3 GAL/SEC. RAPID .s mxaa coouma (Couveunonn)TREATED MILK N GAL/SEC.

United States PatentO TION I Wallace H. Coulter, Chicago, Ill.

Original application August 24, 1951, Serial No. 243,478, new Patent No.2,712,504, dated .luly 5, 1955. Divided and this application February16, 1955, Serial No. 488,665

Claims. (Cl. 99-253) This invention relates generally to the art oftreatment of fluids requiring sterilization or pasteurization andstorage. Such fluids comprise for example foods such as milk which needbe treated by heating in order to render the same safe for consumption.The apparatus is concerned with the heating and the cooling of suchfluids in manners to achieve pasteurization or sterilization in a simpleand economical manner, and yet effectively, with less effect on tastethan heretofore possible.

This application is a division No. 243,478, filed August 24, 1951, nowPatent No. 2,712,504, for Method and Apparatus for Treatment of FluidsRequiringSterilization or Pasteurization.

Many fluids used for human consumption require treatment to destroy orsubstantially reduce the number of microorganisms such as bacteriacarried by the fluids. Pasteurization of dairy products is almostuniversal and sterilization is also very common. Commercial methods ofpasteurization and sterlization are all based upon the concept ofheating the fluid to a given temperature and holding the same at thattemperature to achieve the desired effect. A common method ofpasteurization for example, is to heat raw milk to approximately 140 F.or a little better, for a length of time in the vicinity of half anhour.

It has been known that by increasing the temperature at which the fluidis maintained the time required to accomplish a given treatment ismaterially decreased. The effect on living organisms in milk, forexample, increases at a much greater rate with rising temperatures thanthe effect on taste and other properties. In other words the timefactorfor a given effect on bacteria count can be greatly reduced as thetemperature is increased with an increasingly small effect onpalatibility. For example, milk pasteurization at 170 F. for to secondsis more complete than the older method of 140 F. for 30 minutes and theeffect on taste is less. Temperatures much higher than 170 F. while muchdesired for more complete pasteurization, have heretofore beenimpractical and economically unfeasible.

The logical end to such requirements, namely the application of highertemperatures to achieve treatment desired with decreasing effect ontaste, effectively is thwarted by limitations of presently employedmethods, and indeed all methods known which are economically feasible.The primary obstacle is that the short time intervals cannot be achievedby such prior methods. Although the problem has been understood for manyyears, and although because of the great need many investigators haveexplored the field, no satisfactory solution heretofore has beenpresented to my knowledge. Known methods suffer either from inabilityrapidly to raise and/or lower temperatures or from adverse taste effectscaused by contaminated heat transfer surfaces or electrodes in the caseof direct contact electrical heating.

The invention contemplates a product which is economically heat treated,Whetherpasteurized or sterilized,

from application Serial 2,799,216 Patented July 16, 1957 "ice with lesseffect on taste than heretofore has been believed possible.

Another important factor in the treatment of milk, for example, byheating the same, is the fact that milk is a staple food and isavailable in large quantities at relatively low price. The cost of highspeed sterilization by known methods is expensive and if reflected inthe eventual consumers price will form a very substantial part of thatprice. This factor, handling equipment contaminates easily and must beconstructed to permit easy disassembly thereof has more or less thwartedand retarded speed milk pasteurization and sterilization even by the useof known methods. p v

As far as I have been able to determine, there is no commerciallysuccessful high speed milk sterilization installation in use at thistime despite the great advantages and salutary results that would flowfrom a practical and feasible method. Furthermore, those installationsthat have been producedare either experimental in nature or require suchexpensive and complex apparatus, suchas for example radio frequencyheating, as to make their possibilities of wide-spread adoption andeconomic opera tion quite remote.

My invention principally contemplates apparatus for the economical andpractical heating of perishable fluids to high temperatures forpasteurization or sterilization thereof, such heating to occur in amatter of a fraction of a second and enabling treatment of large volumesof fluid with relatively compact and simple apparatus.

Accordingly the principal object of this invention is to 7 provide suchapparatus.

p A further object of the invention is to accomplish the rapid heatingorcooling of perishable fluids by intermix ing the same with other fluidsof different temperature whereby quickly to achieve a mean temperaturewithout the necessity of using expensive apparatus.

- by virtueof .the highspeedintermixtu're of the fluid of A furtherobject of the invention is to provide apparatus in which a perishablefluid such as milk is passed through a constricted duct and subject tolow frequency current in.

the area to heat same at a rapid rate.

Other objects of the invention are to provide novel apparatus forachieving high speed cooling or heating of.

fluids by intermixture of the same. I

Many other objects of the invention will become apparent as thedescription thereof proceeds. In order to assure a completeunderstanding thereof, I have described preferred embodiments of theapparatus, from which it will be appreciated that numerous variations insize, ar-' rangement, proportion and construction of the various partsthereof are possible without departing from the spirit or scope of theinvention. Consequently in the illustrations I have designated theelements diagrammatically in order not to be limited to any particularconstruction. Fig. 1 is a flow diagram illustrating one form of thelnvention. Fig. 2 is a flow diagram illustrating a second form of theinvention.

Basically, the invention resides in the provision of apparatus capableof mixing fluids for the purpose of achieving high or low temperaturesin very short intervals. The apparatus succeeds also in therecirculation of fluids for the above purpose, achieves high speedheating and is more economical than similar devices heretofore known.The apparatus for quickly heating fluids, such as milk, operates tosubject the fluid to a restrictedelectrical current whilepassingthrougha relatively narrow. conduit at high speed. 1 V In Fig. ,1, there isillustrated a phase of the invention the eflicacy and advantages ofwhich are all engendered together with the fact that milk the widespread use of high two different streams at different temperatureswhereby to affect a temperature change desired.

The additional feature of the system of Fig. 1 is the separation of theincoming fluid into components which are separately treated and thenre-united to produce the final product of the same properties asoriginally, except sterilized or pasteurized by high speed methods. Forexample, in the case of milk, the fluid can be separated into water orwater vapor, and condensed or concentrated milk. The water or watervapor can be heated much higher and easier than the milk because of theprecautions that must be taken with milk to prevent cooked taste, etc.Furthermore there is no time element involved in heating water or incooling the same fairly economically. Its combinations with thecondensed fluid are equally effective for cooling and for heating.

In Fig. 1 I have shown a stream of some untreated fluid entering thesystem, separated into two components, the heat sensitive portion andthe non-heat sensitive portion. For convenience I have presumed thefluid to be raw milk, which separates into the concentrated milk andwater, in the proportions of one to two respectively. Thus, raw milkenters the evaporator 21, and one third passes on to the rapid mixer 24through conduit 25, while two thirds is converted into water vapor andis diverted through conduit 23 to the condenser 22. Half of thecondenser output passes by way of conduit 26 to a heater 27 which mayraise the temperature of the concentrated milk by rapid and thoroughintermixture by any means such as described hereinafter. The waterpasses into the rapid mixer 24 through conduit 30 from the heater 27.

The second half of the condenser output is directed by the duct 28 to acooler 29 which is connected by the duct 33 to another rapid mixer 32.Between the two rapid mixers, the milk is maintained at its hightemperature acquired in rapid mixer 24, passing down a holding duct 31of suitable construction. Thereafter the fluid passes to a conventionalcooler 34 and out the port 35 to storage facilities.

This system illustrates that the separation of the fluid into its heatsensitive and non-heat sensitive components enables the insensitivecomponents to be heated or cooled to temperatures quite a good deal.different from that of the sensitive components, so that the heated orcooled insensitive parts can be used for achieving a product having adesired temperature easily and conveniently.

This is done through high speed mixing in suitable apparatus. Obviouslythe attainment of various temperatures by this means eliminatesapparatus otherwise required which is costly both from cost andmaintenance standpoints.

In the apparatus shown in Fig. 1, it is feasible and desirable undersuitable conditions to use steam instead of hot water. Thus, heater 27may be a steam generator.

For a given amount of moisture considerably greater heat can be carriedby steam than hotv water. Thus, the greater part of the output of thecondenser. 22 may be directed into conduit 28 to give a larger coolingvolume for intermixture with fluid passing into mixer 32.

Another refinement for the apparatus of Fig. 1 consists of pro-heatingof the fluid prior to its entry into the first rapid mixer 24. Suchpre-heating, easily done by conventional methods, may consist inbringing the temperature of the fluid, for example milk, up to 150 160F. It decreases the heat requirements of the hot steam being introducedto the rapid mixer to raise the temperature of the fluid.

In Fig. 2 I have diagrammatically illustrated a device which embodies myinvention and which is highly economical to construct and to maintain.By means of this apparatus, fluid, say for example pre-heated milk,enters at a temperature of say 160 F., is rapidly heated-to 270 F. to300 F. and suddently cooled to 140 F. at a high ratepf speed. This isaccomplished by electrical heating and re-circulation cooling. Thestream enters at the inlet 60 into a chamber 61 whose principal purposeis to house the electrodes 62, the size of which dictates the geometryof chamber 61. The chamber 61 connects with a mixing chamber 63 by meansof a duct 64 which is electrically insulated. In the chamber 63 andsubject to the influence of the fluid passing into chamber 63 fromv theconduit 64 I provide similar electrodes 65. Both sets of electrodes 62and 65 are connected to the ends of the secondary 66 or the transformer67 which is a conventional type transformer having 60 cycle 230 volt A.C. connected across its primary 68. Note that the lead 69 of theelectrodes 65 is preferably grounded.

The heating of the fluid stream is provided by electrical currentflowing through the fluid in the constriction of the conduit 64. Theelectrodes are of cross section area much greater than the cross sectionarea of the conduit 64 to reduce surface current density and surfacecontamination.

The electrodes need not be located in positions where they are incontact with the highest temperatures produced, which arrangementfurther reduces surface contamination. The electrodes may be cooled ifdesired by internally circulated coolant, or, for example in the case ofthe electrodes 65 in chamber 63, the incoming stream of cold fluid fromthe pump, described below, may he directed at said electrodes to reducetheir surface temperature.

Fluid passingthrough the narrow duct 64 is subjected to an electriccurrent which rapidly heats the same. As this heated fluid enters thechamber 63 it will be rapidly and turbulently intermixed with coolerfluid in the chamber and its temperature rapidly dropped, therebyaccomplishing the desired end-namely rapid heating and rapid coolingthereafter. Thorough and complete mixing can be obtained by the use ofdeflecting plates, multiple apertures, cones, etc., all Well-known inthe art. This intermixing is symbolically indicated by arrows shown inthe chamber 63.

In order to obtain the cooling effect, a portion of the fluid in thechamber 63 is constantly being drawn off at 70 at a temperature ofapproximately F. and cooled in a cooler unit 71. The fluid from thecooler passes through the conduit 72 and is forced by the pump 73 backinto the chamber 63 by way of inlet 74. Its temperature of 40 F.combines with the heated fluid coming from the holding duct 64 at atemperature of 270 F. to 300 F. so that the average temperature of thefluid in the chamber 63 is 140 F. more or less.

The insulated duct 64 need not be of uniform cross section throughoutits length. Whether or not of uniform cross section the temperature riseper unit length will remain substantially the same, but the time attemperature will depend upon the cross sectional area because thevelocity of the fluid can be varied by varying the shape of the conduitalong its length. Thus velocity, capacity, and time at which the fluidis maintained at desired temperatures can be controlled in thisapparatus by suitable geometry thereof. The time interval from heatingto cooling is somewhat of the order of .1 second by my apparatus.

The apparatus heretofore described in connection with Fig. 2 involvesthe use of ordinary electric current for heating in contact withexpensive high frequency heating methods which have been proposed. Theapparatus is simple and effective. There is a minimum of surfacecontamination. In short, this type of heating is ideal, since it caneffectively be accomplished in a small volume and at a great speed. Thisparticular method of heating and the apparatus described could be usedas the heater called for throughout the specification herein. Thus, forexample, it could be used at 27 in Fig. 1.

With reference to the re-circulation of fluid through the cooler unit 71a high circulating rate and a very low initial temperature are desirableand will result in greatest efficiency. Furthermore, although the volumeof fluid in the chambers 61 and 63 and in the duct 64 should be kept aslow as possible, the circulating volume in cooling unit 71 and its ductsis not critical. The percentage of fluid recirculated again and againcan be kept low by proper engineering design.

It is believed that the invention has been sufficiently described toenable those skilled in the art to which same pertains to understand andpractice the same. It is contemplated that considerable variation indetails is quite possible without in any way departing from the scope ofthe invention as defined in the appended claims.

What it is desired to secure by Letters Patent is:

1. Apparatus for treating milk in continuous stream which comprises anevaporator having an inlet and outlet, said outlet being connected withrapid mixing means, means for condensing the removed vapor heating thesame and leading at least a portion of the condensate at elevatedtemperature to said rapid mixing means to raise the temperature of milkpassing from the said evaporator to the said mixing means, said mixingmeans being connected with second rapid mixing means, and means forleading another portion of said condensate to said second mixing meansincluding a cooling device, whereby the condensate will be cooled andthereby lower the temperature of the fluid passing to the second mixingmeans from the first mixing means.

2. Apparatus for high speed sterilization or pasteurization of acontinuous stream of fluid which is sensitive to heat comprising, achamber having an inlet port, means connected to feed said fluid in astream through the port, a second chamber having an outlet port, anarrow insulated conduit connected between said chambers, a heatercomprising electrode means in each of said chambers the diameter ofwhich is substantially greater than the crosssectional dimension of theconduit, means for connecting a source of A. C. voltage between saidelectrodes to cause flow of current in a restricted path through saidconduits simultaneously with passage of said fluid through the conduit,to achieve a desired elevated temperature for the fluid in the conduit,and means for controlling the period of time during which the fluid inthe conduit remains at said elevated temperature comprising said conduithaving a predetermined cross-section so related to the length thereof asto establish the velocity of the fluid through the conduit required toachieve said period of time, and means associated with said secondchamber for cooling the heated fluid entering the same.

3. Apparatus as described in claim 2 in which said cooling meanscomprises a third chamber having a cooling device therein, said secondchamber having an additional inlet and outlet, each communicating withsaid third chamber and arranged to effect passage of at least a portionof the heated fluid entering said second chamber out of said secondchamber into said third chamber and thereafter to be cooled and returnedto said second chamber for inter-mixture with heated fluid entering thesecond chamber through said conduit.

I 4. Apparatus as described in claim 3 in which there is a pumpassociated with said third chamber arranged to accelerate the return ofcooled fluid into the second chamber.

5. Apparatus for achieving continuous pasteurization of a stream of milkat a high speed which comprises a coordinated installation including: amilk evaporator unit having an inlet and outlet, means connected withsaid inlet for introducing whole milk into the evaporator, a condenserunit having an inlet connected with the outlet of the evaporator andarranged to receive water vapor from the evaporator and condense thesame, a rapid mixing device having a pair of inlets of which one isconnected with said evaporator to receive concentrated milk from saidevaporator, and a heater including conduit connections between saidcondenser and mixing device arranged to receive therein said condensedvapor, heat the same to a predetermined temperature and introducedesired portions of said condensed vapor at such elevated temperature tosaid mixing device to raise the temperature of the concentrated milktherein sufficiently to affect such pasteurization without adverseeffects on the milk.

Smith et a1. Jan. 1, 1946 Brewer Sept. 4, 1951

